Should I regear?

Hi,
First time poster here. Getting 20" aftermarket wheels and want to mount 275/60/20 Cooper Zeon ltz's. This setup is a 33" tire (+1.5") from the 265/65/18 setup. Will this kill my acceleration and mileage? Should I go with the 275/55/20 Coopers that are 32" tires, only (+.5) from the stock setup? I really like the way the 33" setup looks. Any suggestions, advice? Truck is a 2009 z71 6 speed with 3.42 gearing and 2.5" leveling kit.